The invention relates to a process for the manufacture of articles made from perlite, and particularly construction and thermal insulation materials, especially in the form of bricks or slabs made from perlite.
There are many uses for perlite. These uses can be broken down into three general categories: construction applications, horticultural applications and industrial applications.
Because of the outstanding insulating characteristics and light weight of perlite in its expanded form, it is widely used as a loose-fill insulation in masonry construction. In this application, free-flowing perlite loose-fill masonry insulation is poured into the cavities of concrete block where it completely fills all cores, crevices, water areas and air holes. In addition, to provide thermal insulation, expanded perlite enhances fire ratings, reduces noise transmission and it is rot-, vermin- and termite-resistant. Expanded perlite is also ideal for insulating low temperature and cryogenic vessels. When expanded perlite is used as an aggregate in concrete, a lightweight, fire resistant, insulating concrete is produced that is ideal for roof decks and other applications. Expanded perlite can also be used as an aggregate in Portland cement and gypsum plasters for exterior applications and for the fire protection of beams and columns. Other construction applications include under-floor insulation, chimney lining, paint texturing, gypsum boards, ceiling tiles, and roof insulation boards.
Expanded perlite-simulated stone may be molded to give the appearance of brick, stone or even wood products. A special advantage of expanded perlite simulated stone is that it is light in weight.
Traditional stone and masonry products are heavy and require more expensive structural support. With simulated stone products, traditional framing and supporting materials are usually satisfactory and installation costs can be reduced. A further advantage of lightweight expanded perlite simulated stone products is a reduction in shipping costs and ease of handling. Simulated stone products are excellent for hiding irregular wall surfaces and may be used in a new construction, remodeling and in exterior and interior applications, depending upon the binder used.
U.S. Pat. No. 3,886,076 relates to perlite thermal insulating product and method for producing same. The use of expanded perlite held together by an inorganic binder and a fiber network to form insulation materials is old in the art. As to U.S. Pat. No. 3,886,076 the method of forming a low density corrosion inhibiting thermal insulation product comprises the steps of mixing a wet phase liquids product in a wet phase mixing zone by: adding about 35-52 percent water; adding about 0.33-2.00 percent liquid silicon water repellency material to the water; adding about 13.5-21.0 percent of metallic phosphate binder to the product of the preceding steps. Mixing and agitating is performed in a dry phase mixing zone, whereby about 20.5 to 32 percent expanded perlite having a bulk density from about 2-5 pounds per cubic foot. Not more than 6 percent consist of at least one of sodium tetraborate and sodium silicate and about 1.0-2.5 percent of an inorganic fiber.
The wetted product is placed in a compression zone to form a desired article and the molded product is cured in a heating zone at a temperature of at least 500xc2x0 F. for a period of time sufficient to heat the molded product throughout to a temperature of at least 480xc2x0 F.
SU 157 10 13 describes products made of foamed perlite, but this process involves a liquid solution of sodium and potassium silicate with water created by treating perlite with a chemical solution. The resulting liquid solution is heated to produce a xe2x80x9cfoamedxe2x80x9d perlite, usable only for thermal insulating, not construction, and furthermore the resulting product is not perlite.
U.S. Pat. No. 5,516,351 describes a foamed glass product that can be used as insulation products. The foamed glass product is moisture resistant, fire resistant, corrosion resistant and vermin resistant. In order to improve insulative characteristics, the process comprises providing crushed glass particles and a foaming agent, preferably related from CaCO3 or CaSO4. The pre-treated glass and foaming agent are sized and mixed. The mixed glass and foaming agent are placed in molds and passed through a furnace where the mixture is heated to a foaming temperature and then cooled to produce foamed glass blocks.
Furthermore a non-reactive gas selected from SO3 and CO2 is provided to sweep air away from the mixture during heating. The size of the starting glass particles impacts the insulation properties. A starting glass particle size of approximately 100-700 microns is preferred.
U.S. Pat. No. 3,975,174 relates to a method for manufacture of foamed glass. Finely divided glass, which may have a viscosity between 106 and 107 poises at 950xc2x0 C. to 1100xc2x0 C. and which may be of a composition suitable to conversion into a vitroceramic, is mixed with up to a few percent by weight of a foaming agent including a mixture of SnO2 and SiC, in equimolar proportions or with an excess of SiC. The resulting mixture is heated to 950xc2x0 C. to 1100xc2x0 C. to effect foaming by evolution of CO2 from the foaming agent, and the resulting glass foam is cooled. The nucleation and crystallization steps by which the glass is converted to a vitroceramic may be caused to occur without allowing the foam to return to room temperature.
U.S. Pat. No. 4,992,321 describes a similar method for manufacture of foamed glass.
These known products are relatively expensive and the process to manufacture these products is complicated.
It is an object of the invention to provide a method to manufacture products that are less expensive than prior art products and that can be performed without using any binders, using raw perlite and not expanded perlite.
In accordance with the invention, the process is characterized by the following steps:
a. raw perlite is ground to a particle size  less than 200 xcexcm;
b. silicon carbide as gas forming reagent is ground;
c. said powders are mixed to form a homogeneous mass;
d. then moisturized to a humidity level to display the property of thixotropy;
e. the mixture is vibrated for even distribution in a mold; then upon ceasing vibrations, the mixture solidifies into a molded article;
f. the solidified article is removed from the mold and heated at a temperature between 1200xc2x0 C. and 1350xc2x0 C., and
g. the resulting material is cooled.
The benefit of the claimed process is the fact that binders are not necessary with the effect that the manufactured articles are cheaper than the articles according to prior art. The SiC reacts during heating to form gaseous CO2, and also amorphous SiO2. The SiO2 uses with the perlite. The CO2 generates a foamed structure of the fused perlite material.
Furthermore, the fact that the mixture of perlite, SiC and water can be adjusted to have the property of thixotropy and thus can be formed in the mold. The thixotropic mixture when poured into an unheated mold, becomes more fluid when agitated so as to completely and properly fill the mold cavity. Upon stopping the agitation, the m material sets up and takes on the shape of the mold cavity, and retains the shape when removed from the mold (i.e., is very firm and self-supporting). This xe2x80x9cgreenxe2x80x9d molded article may then be heated apart from the mold as described to react the SiC to form gaseous CO2 and amorphous SiO2, producing a foamed, fused perlite structure.
The resultant material is a hardened foam with evenly-distributed, isolated spherical pores. The regular distribution of pores improves the properties of the foamed perlite material. The foamed perlite material has an outstanding thermal resistance and strength and is gas and water-proof (i.e., the pores are closed) as well as frost and thermo-resistant. This material also is low density and displays low thermal conductivity.